Lesson 2: Free Fall & Air Resistance

​Gravity is an attractive force between all objects that have mass. Gravity causes objects near Earth's surface to fall towards Earth.

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For Example: If you throw a ball in the air the ball will fall back down to the ground due to gravitational forces. ​

​When an object falls, it is because it feels the force of gravity. When objects fall, they will accelerate as they fall. Increasing speed is acceleration.

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Earth gives everything the exact same acceleration. The force that objects feel may be different because they have different masses, but the acceleration on they experience will be exactly the same

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All objects will hit the ground at the same time if dropped from the same height

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​The idea of all objects falling at the same rate seems crazy, because if we were to drop a bowling ball and a feather from the same height right now, the bowling ball would hit the floor first! So how is that possible if gravity gives all objects the same acceleration?

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​The bowling ball would hit the floor before the feather not because of Earth's gravity (which accelerates all falling objects at the same rate), but because air is pushing upwards against the bowling ball and feather in the opposite direction. This force is called air resistance.

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Air resistance is a force that resists an objects motion in air (it pushes upwards against falling objects while gravity pushes downward on objects).

​Note: Objects will not accelerate for forever. When the force of gravity equals the force of air resistance, the object will stop accelerating and will fall at a constant speed, called terminal velocity

​Air resistance will cause objects to land on the ground at different rates.

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The actual amount of air resistance encountered by the object is dependent upon a variety of factors. To keep it simple, it can be said that the two most common factors that have a direct effect upon the amount of air resistance are the speed of the object and the cross-sectional area of the object. Increased speeds result in an increased amount of air resistance. Increased cross-sectional areas (surface area) result in an increased amount of air resistance.

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​Skydivers with similar mass jump from the same plane at the same height.

​At the beginning of the fall, the skydivers will experience the same fall because after they jump, they will accelerate at the same rate until they reach terminal velocity (since they have similar mass and jumped at the same height at the same time) due to gravity and air resistance

​Eventually, the same skydivers will open their parachutes (which are different sizes). The skydiver with the larger parachute will experience more air resistance, therefore start to fall more slowly and take more time to reach the ground than the skydiver with the smaller parachute.